Many integrated circuits require a stable reference voltage for operation. For example, reference voltages are used in data acquisition systems, voltage regulators, virtual grounds, measurement devices, analog-to-digital converters and digital-to-analog converters to name a few. U.S. Pat. No. 5,191,555 assigned to Texas Instruments Incorporated utilizes a reference voltage in a voltage regulator system for a dynamic random access memory, DRAM, application.
A buried-Zener reference is one way to produce a reference voltage. Another way to produce a reference voltage is with a bandgap voltage circuit. Bandgap voltage circuits can operate with a lower supply voltage than buried-Zener references and can also dissipate less power. The above U.S. Pat. No. 5,191,555 illustrates in FIG. 77 a bandgap circuit. Other bandgap reference circuits are illustrated in U.S. Pat. Nos. 5,168,209, 4,939,442, 4,906,863 and 4,362,984 all assigned to Texas Instruments Incorporated. Long term stability of a bandgap voltage reference exceeds that of a buried-Zener reference.
Ideally, a voltage reference circuit would provide a constant voltage regardless of the circuit temperature or its loading conditions. A buried-Zener reference usually has a large amount of temperature dependence, so a bandgap reference is often used when more temperature stability is required. However, any voltage reference, including a bandgap voltage reference, has a certain amount of temperature dependence. A function describing this temperature dependence can be represented as a mathematical polynomial series. Traditional bandgap reference circuits substantially cancel only the first-order term of this function. This, however, still leaves a large amount of variance due to the remaining terms. The 2nd order term, in particular, remains and causes reference inaccuracies as the temperature of the circuit changes. The above U.S. Pat. No. 4,939,442 contains a temperature correction feature. Other correction features are needed.
It is an object of the invention to provide a voltage reference circuit that provides a stable reference over temperature changes.
It is a further object of the invention to provide a circuit to eliminate 2nd order temperature dependency characteristics of bandgap reference circuits.
It is a further object of the invention to provide a bandgap reference voltage circuit that substantially cancels first and second order polynomials.
Other objects and advantages will be apparent to those of ordinary skill in the art having reference to the following specification and drawings.